Cervical intervertebral stabilizer

ABSTRACT

A cervical intervertebral stabilizer for a cervical region of a spine includes: a first surface operable to engage an endplate of a first vertebral bone of a spine; a second surface spaced apart from the first surface and operable to engage an endplate of an adjacent second vertebral bone of the spine; a spring element including at least one of: (i) a helical wound spring; and (ii) a hollow body having at least one slit forming a plurality of annular circumferential helical coils, the spring element being disposed between the first and second surfaces and being operable to provide reactive force in response to compression loads from the first and second vertebral bones, wherein at least some diameters of respective turns of the helical coils differ.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No.: 60/658,345, filed Mar. 3, 2005, the entire disclosureof which is hereby incorporated by reference.

BACKGROUND

The present disclosure generally relates to apparatus and methods fortreatment of spinal disorders using an intervertebral prosthesis whichis disposed in an intervertebral disc space following removal of adamaged or diseased intervertebral disc.

The objective in intervertebral disc replacement or intervertebralstabilization is to provide a prosthetic disc that combines bothstability to support the high loads of the patient's vertebrae andflexibility to provide the patient with sufficient mobility and properspinal column load distribution.

Numerous artificial intervertebral discs for replacing a part or all ofa removed disc have been developed, namely, elastomer discs, ball andsocket discs, mechanical spring discs and hybrid discs. Elastomer discstypically include an elastomer cushion which is sandwiched between lowerand upper rigid endplates. The elastomer discs are advantageous in thatthe elastomer cushion functions similar in mechanical behavior to theremoved intervertebral disc tissue. However, a disadvantage of this disctype is that the elastomer cushion experiences long term in-vivoproblems stemming from microcracking, which detracts from its usefulnessas a replacement option. Furthermore, attachment of the flexibleelastomer cushion to rigid endplates presents additional difficulties.Examples of elastomer discs are disclosed in U.S. Pat. Nos. 5,702,450;5,035,716; 4,874,389; and 4,863,477.

Ball and socket discs typically incorporate two plate members havingcooperating inner ball and socket portions which permit articulatingmotion of the members during movement of the spine. The ball and socketarrangement is adept in restoring “motion” of the spine, but, is poor inreplicating the natural stiffness of the intervertebral disc.Dislocation and wear are other concerns with this disc type. Examples ofball and socket discs are disclosed in U.S. Pat. Nos.: 5,507,816; and5,258,031.

Mechanical spring discs usually incorporate one or more coiled springsdisposed between metal endplates. The coiled springs preferably define acumulative spring constant sufficient to maintain the spaced arrangementof the adjacent vertebrae and to allow normal movement of the vertebraeduring flexion and extension of the spring in any direction. Examples ofmechanical spring discs are disclosed in U.S. Pat. Nos. 5,458,642; and4,309,777.

The hybrid artificial intervertebral disc incorporates two or moreprinciples of any of the aforementioned disc types. For example, oneknown hybrid disc arrangement includes a ball and socket set surroundedby an elastomer ring. This hybrid disc provides several advantages withrespect to load carrying ability, but, is generally complex requiring anumber of individual components. Furthermore, long term in vivodifficulties with the elastomer cushion remain a concern as well as wearof the ball and socket arrangement.

Another type of intervertebral disc prosthesis is disclosed in U.S. Pat.No. 5,320,644. With reference to FIGS. 1-3, the '644 patent discloses aunitary intervertebral disc member 1 made from an elastically deformablematerial. The disc member 1 has parallel slits 5 each arranged at aright angle to the axis of the disc member. The parallel slits 5partially overlap one another to define overlapping regions 6 betweenadjacent slits. The overlapping regions 6 create leaf springs 7 for thetransmission of forces from one vertebral attachment surface to theother. In regions of adjacent slits 5 where they do not overlap thespring action on the leaf springs 7 is interrupted by fixation zones 9of solid prosthesis material. The forces acting on the intervertebraldisc are transmitted from one leaf spring plane to the next leaf springplane via the fixation zones 9. The load paths are inherently abruptwith highly localized transfer of load through the sparsely placedfixation zones 9. There are even instances where the entire load iscarried through a single fixation zone 9 in the center of the disc. Theabrupt load paths can lead to high stress regions, which can detractfrom the appropriate biomechanical performance, i.e., strength,flexibility, and range-of-motion, of the prosthesis.

U.S. Pat. No.: 6,296,664 discloses an intervertebral prosthesis having adisc member defining a longitudinal axis extending the height of thedisc member and a lateral axis transverse to the longitudinal axis. Thedisc member includes an exterior wall which has a slit defined therein.The slit defines a longitudinal component of direction and a lateralcomponent of direction. Preferably, the exterior wall includes aplurality of helical slits, adjacent slits being disposed in at leastpartial overlapping relation to define an overlapping region. Uponinsertion of the disc member within the intervertebral space with thesupport surfaces in contacting engagement with respective vertebralportions of the adjacent vertebrae, forces exerted by the vertebralportions on the support surfaces are transferred along the exterior wallthrough the overlapping region.

All of the above intervertebral devices suffer from common problems, forexample, they are limited in the reaction forces that they produce inresponse to compressive forces. For instance, once mechanical springdiscs bottom out, there is no further articulation provided. This isundesirable in some applications. Further, the above described devicesare not suitable for posterior implantation. Still further the abovedescribed devices are difficult to implant, reposition, or remove.

Thus, there has been discovered a need for a new intervertebralstabilizer.

SUMMARY OF THE INVENTION

In accordance with one or more embodiments of the present invention, acervical intervertebral stabilizer for a cervical region of a spineincludes: a first surface operable to engage an endplate of a firstvertebral bone of a spine; a second surface spaced apart from the firstsurface and operable to engage an endplate of an adjacent secondvertebral bone of the spine; a spring element including at least one of:(i) a helical wound spring; and (ii) a hollow body having at least oneslit forming a plurality of annular circumferential helical coils, thespring element being disposed between the first and second surfaces andbeing operable to provide reactive force in response to compressionloads from the first and second vertebral bones, wherein at least somediameters of respective turns of the helical coils differ.

Those of the turns having larger diameters are preferably disposedtowards the first and second surfaces and those of the turns havingsmaller diameters are centrally located between the turns having largerdiameters. Alternatively or in addition, the cross-sectional profiletaken through the spring element is preferably at least partiallyhourglass shaped. Alternatively, the cross-sectional profile takenthrough the spring element is a multiple hourglass shape.

Other aspects, features, advantages, etc. will become apparent to oneskilled in the art when the description of the preferred embodiments ofthe invention herein is taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purposes of illustrating the various aspects of the invention,there are shown in the drawings forms that are presently preferred, itbeing understood, however, that the invention is not limited to theprecise arrangements and instrumentalities shown.

It is noted that the numerous figures herein are drawn substantially toscale at least in terms of the relationships among the elements of theparticular views shown.

FIGS. 1-2 illustrate perspective and side (or lateral) views,respectively, of an intervertebral stabilizer in accordance with one ormore embodiments of the present invention;

FIGS. 3-4 illustrate perspective views of certain spring features of theintervertebral stabilizer of FIGS. 1-2;

FIG. 5 is a side view of an intervertebral stabilizer in accordance withone or more further embodiments of the present invention;

FIGS. 6-8 illustrate perspective, side (or lateral), and anterior views,respectively, of an intervertebral stabilizer in accordance with one ormore further embodiments of the present invention;

FIGS. 9-10 illustrate perspective and anterior views, respectively, ofthe intervertebral stabilizer of FIGS. 6-8 in use;

FIGS. 11-13 illustrate perspective, side, and anterior views,respectively, of an intervertebral stabilizer in accordance with one ormore further embodiments of the present invention;

FIG. 14 is a sectional view of an intervertebral stabilizer inaccordance with one or more further embodiments of the presentinvention;

FIGS. 15-17 illustrate perspective, anterior, and side views,respectively, of an intervertebral stabilizer element in accordance withone or more further embodiments of the present invention;

FIGS. 18-20 illustrate perspective, side, and cross-sectional views,respectively, of an intervertebral stabilizer in accordance with one ormore further embodiments of the present invention;

FIGS. 21-22 illustrate perspective and side views, respectively, of anintervertebral stabilizer in accordance with one or more furtherembodiments of the present invention;

FIGS. 23-24 illustrate perspective and side views, respectively, of anintervertebral stabilizer in accordance with one or more furtherembodiments of the present invention;

FIGS. 25-26 illustrate perspective and side views, respectively, of anintervertebral stabilizer in accordance with one or more furtherembodiments of the present invention;

FIG. 27 is a perspective view of an intervertebral trial in accordancewith one or more embodiments of the present invention;

FIG. 28 is a perspective view of an alternative configuration of aspacer for the intervertebral trial of FIG. 27;

FIGS. 29-31 illustrate perspective, top, and lateral cross-sectionalviews, respectively, of an insertion tool suitable for implanting one ormore of the intervertebral stabilizers herein;

FIG. 32 is a perspective view of a wedge ramp insertion tool suitablefor assisting in the implantation of one or more of the intervertebralstabilizers discussed herein;

FIGS. 33-37 are perspective views illustrating an implantation processutilizing the wedge ramps and insertion tools of FIGS. 29-32; and

FIGS. 38-39 illustrate perspective and side views of an extraction toolsuitable for repositioning and/or extracting one or more of theintervertebral stabilizers discussed herein.

DETAILS OF THE EMBODIMENTS OF THE INVENTION

FIGS. 1-2 illustrate an embodiment of a spinal intervertebral stabilizer50 in accordance with one or more aspects of the present invention. Thestabilizer 50 is sized and shaped to fit in the intervertebral spacebetween adjacent vertebral bones of the spine. It is understood that thesize and shape of the stabilizer 50 may be adapted to fit in anintervertebral space at any level of the spine, such as the cervicalspine, thoracic spine, or lumbar spine. The stabilizer 50 is sized andshaped to be inserted into the inter-vertebral space from an anteriordirection. The stabilizer 50 includes an upper surface 52 of a firstmember 53 and a lower surface 54 of a second member 55 that are operableto engage end plates of the respective vertebral bones. A spring elementin the form of a helical coil 56 is interposed between the upper andlower surfaces 52, 54 of the first and second members 53, 55.

The helical coil 56 includes at least one first segment 56A having afirst diameter and at least one second segment 56B having a seconddiameter. In the embodiment shown, two second segments 56B are disposedaxially with respect to a single first segment 56A, which is interposedbetween the second segments 56B. As shown, the stabilizer 50 may providesome movement in compressive and/or expansion directions due to thespaces between the respective turns of the second segments 56B of thehelical coil 56. These spaces between the turns may be adjusted toprovide differing amounts of compressive or expansion movement of thestabilizer 50. The compressive and expansion movement may also beadjusted by varying material properties of the segments 56B. Thestabilizer 50 may also provide some movement in bending due to the firstsegment 56A of the helical coil 56. More particularly, the first andsecond segments 56A, 56B of the stabilizer 50 permits movement as todisplacement, rotation, subluxation, flexion, extension, bending, or anycombination thereof.

Among the movements permitted by the stabilizer 50 is flexing bycollapsing one side of the stabilizer 50 and expanding the other side.The degree of collapsing and expanding of the stabilizer 50 may bevaried depending on the spring properties of the first and secondsegments 56A, 56B of the helical coil 56. In this regard, reference isnow made to FIGS. 3-4, which are conceptual illustrations of the springproperties of the first and second segments 56A, 56B, respectively, ofthe helical coil 56 as if employed separately. As shown in FIG. 3, therelatively small spring diameter of the first segment 56A promotesbending (deflection f) because the deflection f is inverselyproportional to an outside diameter D of the turns of the first segment56A. This may be expressed as follows: f=k/D, where k is the springconstant of the spring. Thus, the smaller the diameter D of the firstsegment 56A, the more deflection f is achieved and vice verse. Notably,the first segment 56A simultaneously prohibits compression and expansion(B) because such movement is directly proportional to the diameter D.This may be expressed as follows: B=k·D. In contrast, as the secondsegment 56B has a relatively larger diameter spring, it promotescompression and expansion, and inhibits bending.

The resultant functionality of the helical coil 56 is that one or moreof the segments of the coil 56 permit compression/expansion and inhibitflexion (such as segments 56B), while one or more other of the segmentspermit flexion and inhibit compression/expansion (such as segment 56A).Thus, the first and second segments 56A, 56B of the stabilizer 50 permitmovement as to displacement, rotation, subluxation, flexion, extension,bending, or any combination thereof.

The functionality of the varying diameter coil segments 56A, 56B may beadapted in an embodiment with a spring element having a more graduallychanging diameter as is illustrated in FIG. 5. This embodiment includesa spinal intervertebral stabilizer 80 in accordance with one or moreaspects of the present invention. The stabilizer 80 is sized and shapedto fit in the intervertebral space between adjacent vertebral bones ofthe spine, and as with one or more other embodiments herein, it isunderstood that the size and shape of the stabilizer 80 may be adaptedto fit in an intervertebral space at any level of the spine, such as thecervical spine, thoracic spine, or lumbar spine. As with the stabilizer50, the stabilizer 80 includes a spring element having a plurality ofsegments, some of which promote compression/expansion, while otherspromote flexion. The spring element is in the form of a helical coil ofhourglass cross section. These and other properties of the stabilizer 80will be discussed in more detail herein with reference to severalspecific examples.

FIGS. 6-8 illustrate an embodiment of a spinal intervertebral stabilizer100. As best seen in FIGS. 9-10, the stabilizer 100 is sized and shapedto fit in the intervertebral space between adjacent vertebral bones 10,12 of the spine. It is understood that the size and shape of thestabilizer 100 may be adapted to fit in an intervertebral space at anylevel of the spine, such as the cervical spine, thoracic spine, orlumbar spine. The stabilizer 100 is sized and shaped to be inserted intothe inter-vertebral space from an anterior direction.

The stabilizer 100 includes an upper surface 102 and a lower surface 104that are operable to engage the end plates 14, 16 of the respectivevertebral bones 10, 12. The body 106 of the stabilizer 100 is ofgenerally cylindrical construction. As best seen in FIGS. 7-8, across-sectional profile of the body 106 is hourglass shaped. The body106 also includes a spring element in the form of a helical coil inwhich a continuous or substantially continuous slot 108 extendshelically from a terminal end 108A adjacent the first surface 102 to aterminal end 108B adjacent the second surface 104. The slot 108 providesthe stabilizer 100 with a spring capability by creating respective turnsor coils of the helical coil. In alternative embodiments, the springfeature of the body 106 may be formed from a helical wound spring, suchas of circular, rectangular, or other shape cross-sectionalconfiguration. In a preferred embodiment, the body 106 is formed of asubstantially solid cylindrical hollow body in which the helical coilsare formed from the substantially continuous slot 108 that is cut intothe body 106 through to the hollow portion 120 thereof.

In a preferred embodiment, the upper surface 102, the lower surface 104,and the body 106 are formed as an integral element, e.g., ofsingle-piece construction.

At rest, the stabilizer 100 preferably takes the orientation shown. Thespring features of the body 106 are preferably designed such that thestabilizer 100 maintains a minimum distance between the vertebral bones10, 12 inasmuch as the surfaces 102, 104 may not be compressed towardsone another beyond a minimum distance. As shown, the stabilizer 100provides some movement in the compressive direction because the slot 108provides some distance between the “coils” of the spring feature. Thisdistance or space between the coils may be adjusted to provide differingamounts of compressive movement of the stabilizer 100. For example, thespace may be at a minimum, such as zero, which would inhibit anycompressive movement of the stabilizer 100 and also the vertebralbodies.

Although the stabilizer 100 limits the distance between the vertebralbodies, it permits some movement as to displacement, rotation,subluxation, flexion, extension, bending, or any combination thereof.For example, the designed permits longitudinal or flexing by collapsingone side of the stabilizer 100 and expanding the other side. Dependingon the amount of space provided between the coils of the spring featureof the body 106, the center of rotation associated with flexing may bewell outside the inter-vertebral space, potentially one to five inchesor more outside the inter-vertebral space.

As best seen in FIG. 7, the upper surface 102 includes a peripheral edge112 that overhangs at least one coil of the body 106, and preferablyoverhangs all of the coils of the body 106. Similarly, the lower surface104 includes a peripheral edge 114 that overhangs at least one coil ofthe body 106, and preferably all of the coils of the body 106. In thisregard, a moment arm Ma is defined by a lateral distance between anouter surface of the at least one coil 110 of the body 106 and theperipheral edge 112 of the upper surface 102. The same or another momentarm may also be defined in terms of the peripheral edge 114 of the lowersurface 104 and the outer surface of the coil 110. Those skilled in theart will appreciate that the moment arm Ma may also be defined in termsof the point at which the slot 108 collapses and respective adjacentcoils engage one another. Irrespective of how the moment arm is defined,a compressive force Fc acting on, for example, at least a portion of theperipheral edge 112 and any portion of the lower surface 104 tends tocollapse the spring of the body 106 and full compression of the springresults in closure of the slot 108 in the vicinity of the force Fc suchthat adjacent coils engage one another. Further compressive force Fcwill work in conjunction with the moment arm Ma such that portions ofthe coils on an opposite side of the spring of the body 106 from theengaged coils tends to expand.

A surgeon is preferably provided with a plurality of different sizedintervertebral stabilizers 100 that he or she may utilize to fit theparticular physiology of the patient. In general, relatively largerintervertebral stabilizers 100 will be useful in the lumbar region ofthe spine, smaller sized intervertebral stabilizers 100 will be usefulin the thoracic region of the spine, and still smaller sizedintervertebral stabilizers 100 will be useful in the cervical spine. Byway of example, it is preferred that a height H of the intervertebralstabilizer 100 (e.g., measured between the upper and lower surface 102,104) is between about 8.0 mm to about 18.0 mm for use in the lumbarregion of the spine. More particularly, a number of different sizedintervertebral stabilizers 100 are preferably available to the surgeon,such as having a height of between (i) about 8.0 mm to 10.0 mm; (ii)about 10.0 mm to about 14.0 mm; and (iii) about 14.0 mm to about 18.0mm.

The spring feature of the body 106 is preferably formed utilizing about1.0 slot or 2.0 coils when the height of the intervertebral stabilizer100 is about 8.0 mm to about 10.0 mm. In this context, about two turnsor coils are created by one slot traversing at least partially aroundthe body 106. The spring feature of the body 106 is preferably formedfrom about 2.0 slots or 3.0 coils when the height of the intervertebralstabilizer 100 is about 10.0 mm to about 14.0 mm. Additionally, thespring feature of the body 106 is preferably formed from about 3.0 slotsor 4.0 coils when the height of the intervertebral stabilizer 100 isabout 14.0 mm to about 18.0 mm.

With reference to FIGS. 11, 12, and 13, perspective, side, and anteriorviews, respectively, of an intervertebral stabilizer 100A areillustrated. The intervertebral stabilizer 100A is preferably used inthe cervical spine. In this regard, the height of the intervertebralstabilizer 100A is preferably between about 6.0 mm to about 9.0 mm. Thesurgeon is preferably provided with a plurality of different sizedintervertebral stabilizers 100A for the cervical region of the spine. Inparticular, an intervertebral stabilizer 100A having a height of about5.0 mm to about 7.0 mm is formed in which the spring feature of the body106 is formed utilizing about 3.0 slots or 4.0 coils. In a furtherembodiment of the intervertebral stabilizer 100A, the height is about7.0 mm to about 9.0 mm and the spring feature of the body 106 is formedfrom about 4.0 slots or 5.0 coils.

As best seen in FIGS. 6 and 11, the intervertebral stabilizers 100, 100Amay include one or more bone adhesion facilitating elements 121 operableto promote bone adhesion to at least one of the upper and lower surface102, 104. As shown, the bone adhesion facilitating elements 121 mayinclude one or more spikes oriented in any number of directions andbeing of generally triangular cross-section. Other embodiments of theinvention contemplate that the bone adhesion facilitating elements areformed from one or more keels extending from the upper and/or lowersurface 102, 104; and/or from one or more roughening elements (such asdimpling or knurling) on one or both of the upper and lower surfaces102, 104.

In one or more embodiments, the hollow portion 120 of the body 106 mayextend from the upper surface 102 to the lower surface 104 unimpeded.With reference to FIG. 14, in one or more further embodiments, thehollow portion 120 may include a membrane 122 disposed in the passageand substantially closing off the passage to inhibit bone growththerethrough. Preferably, the membrane 122 is formed as an integralelement of the body 106. For example, the hollow portion 120 may beformed from first and second hollow portions 120A, 120B that do not passall the way through the body 106. With or without the membrane 122, thehollow portion 120 is preferably of hourglass shape.

As best seen in FIG. 14, with or without the membrane 122, the shape ofthe hollow portion 120 is preferably also hourglass shaped. Although thepresent invention is not limited to any particular theory of operation,it is believed that such an hourglass shaped hole or hollow portion 120maximizes or at least significantly increases the moment arm Ma, theoffset between the compressive load application point at the peripheraledge (e.g. at 112A in FIG. 1) and the outer surface of the springelement (e.g., at 110).

Reference is now made to FIGS. 15-17, which illustrate perspective,anterior, and side views, respectively, of an alternative embodiment ofa spinal inter-vertebral stabilizer element 100B. The stabilizer element100B may include some or all of the features discussed hereinabove withrespect to the stabilizers 100 and/or 100A. Respective peripheral edges142 and 144 of the upper and lower surfaces 132, 134 circumscribe akidney shape. In use, two of the stabilizer elements 100B (mirror imagesof one another) are inserted into a single intervertebral space suchthat an overall envelope created by at least portions of the peripheraledges 142 and/or 144 of the two stabilizer element 100B approximate theshape of the intervertebral space.

The intervertebral stabilizer 100B is preferably sized and shaped to beinserted posteriorly or transversely into the intervertebral space. Inthis regard, the stabilizer element 100B preferably includes a length Lmeasured along an anterior-to-posterior direction of the spine and awidth W along a lateral direction of the spine. The width of thestabilizer element 100B is preferably smaller than the length thereofsuch that the stabilizer 100B may be implanted from the posterior ortransverse-posterior direction into the intervertebral space.

As with the intervertebral stabilizer 100 of FIGS. 6-8, theintervertebral stabilizer element 100B is preferably provided to thesurgeon in a number of different sizes (for each mirror image thereof)to accommodate different levels in the spine and/or different physiologyof a given patient. It is preferred that the height H of the stabilizerelement 100B (e.g., measured between the upper and lower surface 132,134) adheres to the various dimensions discussed hereinabove withrespect to the stabilizer 100. Further, the height of the stabilizerelement 100B is preferably characterized as being one of: (i) about 7.0mm to about 15.0 mm when the spring element of the body 136 includesabout 1.0 slot or 2.0 coils; (ii) about 11.0 mm to about 20.0 mm whenthe spring element of the body 136 includes about 2.0 slots or 3.0coils; and (iii) about 13.0 mm to about 26.0 mm when the spring elementof the body 136 includes about 3.0 slots or 4.0 coils.

Reference is now made to FIGS. 18-20, which are perspective, side andcross-sectional views, respectively, of a further embodiment 100C of thepresent invention. In many ways, the stabilizer 100C is substantiallythe same as the stabilizer 100 of FIGS. 6-8. Indeed, the stabilizer 100Cincludes an upper surface 102 and a lower surface 104 that are operableto engage the end plates 14, 16 of the respective vertebral bones 10,12. The body 106 of the stabilizer 100C is of generally cylindricalconstruction and includes a spring element in the form of a helical coilin which a continuous or substantially continuous slot 108 extendshelically from a terminal end adjacent the first surface 102 to aterminal end adjacent the second surface 104. Unlike the priorembodiments, the cross-sectional profile of the body 106 is onlypartially hourglass shaped. Indeed, the body 106 includes asubstantially flat portion 106′ that does not have an hourglass contour.The detailed discussion above regarding the full hourglass-shaped body106 applies with equal weight here, although those skilled in the artwill appreciate that the principles of operation of the fullhourglass-shaped body 106 may also be inherently extended. A hollowportion or aperture 120 preferably extends from the surface 102 to thesurface 104. The hollow portion 102 may also include the membrane 122(FIG. 14), and/or may also be hourglass shaped.

Reference is now made to FIGS. 21-22, which are perspective and sideviews, respectively, of a further embodiment of the present invention.The stabilizer 100D includes an upper surface 102 and a lower surface104 that are operable to engage the end plates of respective vertebralbones. The body 106 of the stabilizer 100D includes a plurality ofhourglass shaped segments 106A, 106B, etc. (two such segments beingshown for illustration). As with some of the prior embodiments, thecross-sectional profile of the body 106 is hourglass shaped; however,this embodiment of the invention include multiple hourglass shapes inaxial alignment. A hollow portion or aperture 120 preferably extendsfrom the surface 102 to the surface 104. The hollow portion 102 may alsoinclude the membrane 122 (FIG. 14), and/or may also be hourglass shaped.The detailed discussion above regarding a single hourglass-shaped body106 applies with equal weight here, although those skilled in the artwill appreciate that the principles of operation of the singlehourglass-shaped body 106 may also be inherently extended.

As best seen in FIG. 22, the intervertebral stabilizer 100D may includeone or more bone adhesion facilitating elements 121 operable to promotebone adhesion to at least one of the upper and lower surface 102, 104.The bone adhesion facilitating elements 121 may include one or morespikes oriented in any number of directions and being of generallytriangular cross-section. Other embodiments of the invention contemplatethat the bone adhesion facilitating elements are formed from one or morekeels extending from the upper and/or lower surface 102, 104; and/orfrom one or more roughening elements (such as dimpling or knurling) onone or both of the upper and lower surfaces 102, 104. Alternatively orin addition, the stabilizer 100D may include a flange 160 of generallytransverse orientation with respect to the end surface (e.g., surface102) and operable to engage a sidewall of the vertebral bone by drivingone or more screws through aperture (s) 162 of the flange 160 into thevertebral bone. As shown, the stabilizer 100D includes one or more boneadhesion facilitating elements 121 (e.g., spikes) on the surface 104 anda flange 160 extending from the surface 102. Other combinations may beemployed without departing from the spirit and scope of the invention.

Reference is now made to FIGS. 23-24, which are perspective and sideviews, respectively, of a further embodiment of the present invention.While the embodiments of the invention discussed above may be used tostabilize a single pair of vertebral bones, the stabilizer 100E isoperable to accommodate a larger space for multiple levels ofintervertebral bones. The stabilizer 100E includes an upper surface 102and a lower surface 104 that are operable to engage the end plates ofrespective vertebral bones. The vertebral bones, however, need not beadjacent to one another; rather, a vertebral bone of an interveninglevel may be removed and the remaining vertebral bones may be stabilizedusing the stabilizer 100E. The body 106 of the stabilizer 100E includesa plurality of axially aligned, hourglass shaped segments 106A, 106B(two such segments being shown for illustration). A further segment 106Cis interposed between the hourglass segments 106A, 106B, where thesegment 106C does not include a spring feature. The segment 106Caccounts for the removed vertebral bone. As shown, the stabilizer 100Eincludes one or more bone adhesion facilitating elements 121 (e.g.,spikes) on the surface 104 and a flange 160 extending from the surface102. Other combinations may be employed without departing from thespirit and scope of the invention.

Reference is now made to FIGS. 25-26, which are perspective and sideviews, respectively, of a further embodiment 100F of the presentinvention. As with the stabilizer 100E of FIGS. 23-24, the stabilizer100F is operable to accommodate multi-level stabilization. Thestabilizer 100F includes an upper surface 102 and a lower surface 104that are operable to engage the end plates of respective vertebralbones. Again, the vertebral bones are not adjacent to one another;rather, two or more vertebral bones of intervening level(s) may beremoved and the remaining vertebral bones may be stabilized using thestabilizer 100F. The body 106 of the stabilizer 100F includes aplurality of axially aligned, hourglass shaped segments 106A, 106B, 106E(three such segments being shown for illustration). Further segments106C and 106D are interposed between the hourglass segments 106A, 106Band between 106B, 106E, respectively. The segments 106C and 106D do notinclude spring features as they accounts for the removed vertebralbones. As shown, the stabilizer 100E includes a flange 160 on thesurfaces 102, 104 to secure the stabilizer 100F. It is noted thatfurther bone adhesion promoting elements may also be employed withoutdeparting from the spirit and scope of the invention.

Reference is now made to FIGS. 27-39, which illustrate variousinstrumentations for implanting, for example, the intervertebralstabilizer 100 into a patient. FIG. 27 is a perspective view of anintervertebral trial 200 which is preferably used to prepare the endplates 14, 16 of the intervertebral bones 10, 12, respectively, prior toimplantation of the stabilizer 100. More particularly, after anteriorincision and access to the intervertebral bones 10, 12 is obtained, theintervertebral space between the end plates 14, 16 is evacuated byremoving the disk, some connecting tissue, etc. Next, the trial 200 isutilized to abrade the end plates 14, 16 of the vertebral bones 10, 12.The trial 200 includes a handle 202 and at least one spacer element 204.In a preferred embodiment, another spacer 206 (preferably of differentsize or character) is included at an opposite end of the handle from thespacer 204. For purposes of brevity, reference will now be made only tospacer element 204, it being understood that the description of spacer204 may be applied to spacer 206 with equal force.

The spacer element 204 depends from the handle 202 and is preferablysized and shaped to fit in the intervertebral space between therespective end plates 14, 16. The spacer element 204 includes an uppersurface 208 and a lower surface 210 that are spaced apart by a heightdimension. Preferably, the height is of a sufficient magnitude to atleast slightly expand the intervertebral space when the spacer element204 is urged between the end plates 14, 16. More particularly, the uppersurface 208 preferably engages the end plate 14, while the lower surface210 engages the end plate 16.

At least one of the upper and lower surfaces 208, 210 preferablyincludes a roughening element 212, such that insertion of the spacerelement 204 into the intervertebral space abrades the associated endplate in preparation for implantation of the intervertebral stabilizer100. In a preferred embodiment, both the upper and lower surface 208,210 include a roughening element 212 such that insertion of the spacerelement 204 into the intervertebral space simultaneously abrades bothend plates 14, 16. Preferably, the roughening element is formed fromsubstantially sharp knurling disposed on the respective surfaces 208,210.

With reference to FIG. 28 the shape of the spacer element 204 may bekidney shaped for posterior or lateral implantation.

In a preferred embodiment, the surgeon is provided with a plurality oftrials 200, each with differing sized spacer elements 204, 206, suchthat the surgeon may choose an appropriate sized trial 200 in order toprepare the intervertebral space for implantation. In addition, theplurality of trials 200 may include differing levels of roughness, forexample, by adjusting the sharpness and magnitude of the knurling 212.The abrasion of the end plates 14, 16 facilitates bone growth and secureengagement of the upper and lower surfaces 102, 104 of the stabilizer100 upon implantation into the intervertebral space.

With reference to FIGS. 29, 30 and 31, an insertion tool 250 ispreferably utilized to implant an intervertebral stabilizer, such as oneor more of the intervertebral stabilizers discussed above into theintervertebral space. For purposes of discussion, reference to thestabilizer 100 of FIGS. 6-8 will be made, it being understood that thedescription may be applied to the other stabilizer embodimentscontemplated herein.

The insertion tool 250 includes a handle 252 and a head 254. The head254 is operable to releasably engage the intervertebral stabilizer 100such that the surgeon may manipulate the position of the stabilizer 100by way of the handle 252 in order to urge the stabilizer 100 into theintervertebral space. As best seen in FIG. 31, the head 254 includes atleast a pair of spaced apart pins 256, 258 that facilitate theengagement between the head 254 and the intervertebral stabilizer 100.

As best seen in FIGS. 6 and 8, the intervertebral stabilizer 100 (or anyof the other embodiments herein) may include at least a pair of spacedapart apertures 150, 152 operable to receive the pins 256, 258 of theinsertion tool 250. As shown, a longitudinal axis A of the stabilizer100 is normal to the first and second surface 102, 104 and the apertures150, 152 extend transversely with respect to the longitudinal axis A.The apertures 150, 152 may extend at least partially into the body 106,although it is preferred that the apertures 150, 152 extend all the waythrough the body 106 into the hollow portion 120. As the stabilizer 100is intended for anterior implantation, the apertures 150, 152 arepreferably disposed on an anteriorly directed side of the body 106.Thus, as best seen in FIGS. 29 and 30, the insertion tool 250 engagesthe intervertebral stabilizer 100 from the anterior direction such thatthe surgeon may urge the stabilizer 100 into the intervertebral spacefrom the anterior direction.

Further, the apertures 150, 152 are preferably positioned longitudinalwith respect to one another, parallel to the longitudinal axis A. Forexample, the aperture 150 is disposed toward the first surface 102 andthe second aperture 152 is disposed toward the second surface 104. Asshown in FIG. 8, the apertures 150, 152 are entirely within the body 106such that they form a closed interior surface. In a preferredembodiment, the apertures 150, 152 are disposed at terminal ends 108A,108B of the slit 108 such that the slit 108 communicates with theinterior of the respective apertures 150, 152.

As shown in FIGS. 11 and 13, an alternative embodiment may provide apair of apertures 154, 156 that extend only partially into the body 106such that respective slots are formed at the first and second surfaces102, 104. In a preferred embodiment, one or more spikes, keels, orroughening elements 121 are disposed at least partially along the slot.For example, when a pair of spikes 121 are provided along the slot, adual function may be enjoyed, namely: (i) the spikes assist in formingthe slot, thereby facilitating engagement between the insertion tool 250and stabilizer 100A; and (ii) once implanted, the stabilizer 100A isencouraged to remain in the implanted position owing to the spikes 121engaging the respective end plates 14, 16.

As best seen in FIGS. 15 and 16, one or more apertures 158 (one aperturebeing shown for simplicity) may be provided in the body 136 of thestabilizer element 100B in order to assist in the implantation of theelement 100B into the intervertebral space from a posterior ortransverse posterior direction. Thus, the aperture 158 is posteriorlydirected.

Turning again to FIGS. 29-31, the pins 256, 258 are preferably flexiblein a direction parallel to the longitudinal axis A (FIG. 6) of thestabilizer 100. Thus, assuming that the pins are spaced apart at anappropriate distance, the apertures 150, 152 urge the pins 254, 258apart when the head 254 engages the stabilizer 100. Similarly, dependingon the spring constant of the spring feature of the stabilizer 100 ascompared with the flexibility of the pins 254, 258, the pins 254, 258may urge the upper and lower surface 102, 104 together when the head 254engages the stabilizer 100.

As best seen in FIG. 31, a height of the head 254 (measured parallel tothe longitudinal axis A) is preferably less than the height of thestabilizer 100. This insures that the head 254 does not interfere withthe implantation of the stabilizer 100 in the intervertebral space. Asthe cross-sectional profile of the body 106 is hourglass shaped, thehead 254 is preferably sized such that it at least partially enters intothe depression defined by the hourglass shape of the body 106. It ispreferred that the contour of the head 254 matches the curvature of thebody 106 as is best seen in FIG. 31. Further, the head 254 preferablyflairs out in a transverse (e.g., perpendicular) direction to thelongitudinal axis A and terminates at respective prongs 260, 262 thatprovide lateral engagement with the body 106 of the stabilizer 100. Thisadvantageously assists in the lateral stability of the engaged insertiontool and stabilizer 100 as the stabilizer 100 is implanted into theintervertebral space.

Reference is now made to FIGS. 32 and 33, which illustrate a furtherinsertion tool for implantation of the intervertebral stabilizer 100from an anterior direction. Again, for purposes of discussion, referenceto the stabilizer 100 of FIGS. 6-8 will be made, it being understoodthat the description may be applied to the other stabilizer embodimentscontemplated herein. The insertion tool preferably includes first andsecond elongate ramps 300, 302 that cooperate to assist in theimplantation of the stabilizer 100 into the intervertebral space. Asingle ramp 300 is shown in FIG. 32, it being understood that the ramp302 is substantially similar as will be evident to one of ordinary skillin the art after reviewing this specification. Each elongate ramp 300,302 includes a proximal end 304 and a distal end 306. The distal end 306is sized and shaped for insertion into the intervertebral space in orderto engage one of the end plates. The end 306 preferably includes a stopmember 308 that is operable to engage the associated intervertebral boneand to limit a distance that the distal end 306 may enter into theintervertebral space. As best seen in FIG. 33, the stop 308 abuts thevertebral bone 10.

In use, the first and second ramps 300, 302 are disposed opposite to oneanother to define upper and lower surfaces 320, 322 when the distal ends306 thereof are inserted into the intervertebral space. The proximalends 304 of the ramps 300, 302 are preferably fixed positionally withrespect to one another by a clamp member 310. More particularly, each ofthe distal ends 304 includes a bore 312 into which an end of the clamp310 may be inserted. The clamp 310 is preferably of a U-shape in orderto fix the relative positions of the proximal ends 304 with respect toone another. It is noted that the surgeon may omit use of the clamp ifhe or she insures that the proximal ends 304 of the ramps 300, 302 arefixed with respect to one another by clamping same with his or her hand.

With reference to FIGS. 34 and 35, the intervertebral stabilizer 100 ispreferably slid along the surfaces 320, 322 from the proximal end 304toward the distal end 306. In a preferred embodiment, respectiveprotrusions, such as spikes 121 are spaced apart on at least one of theupper and lower surface 102, 104 of the stabilizer 100 at a distance toaccommodate a width of the ramps 300, 302. Advantageously, slideableengagement of the spikes 121 with respective lateral edges 324, 326 ofthe ramps 300, 302 insure that the stabilizer 100 slides properly alongthe surfaces 320, 322 and remains between the ramps 300, 302.Preferably, the lateral edges 324, 326 are chamfered in an appropriateway to complement the contour of the spikes 121 to improve slideabilityand/or stability of the intervertebral stabilizer 100 as it slides alongthe ramps 300, 302.

As best seen in FIG. 35, the substantially fixed positions of the distalends 304 of the ramps 300, 302 and the sliding intervertebral stabilizer100 at least opens the intervertebral space owing to the lever action ofthe ramps 300, 302. It is also preferred that simultaneously with theopening of the intervertebral space, the intervertebral stabilizer 100is compressed. It is noted that if the surgeon chooses to manually urgethe distal ends 304 of the ramps 300, 302 together while theintervertebral stabilizer 100 is interposed between the proximal anddistal ends 304, 306 of the ramps 300, 302, then additional opening ofthe intervertebral space and/or compression of the intervertebralstabilizer 100 may be obtained. Of course, the surgeon would have toperform this manual operation without the clamp 310.

As best seen in FIG. 36, appropriate sliding of the intervertebralstabilizer 100 along the ramps 300, 302 utilizing the handle 252 of theinsertion tool 250 results in proper positioning of the intervertebralstabilizer 100 within the intervertebral space. Thereafter, the ramps300, 302 may be removed such that the intervertebral stabilizer 100engages the respective end plates 14, 16 of the adjacent vertebral bones10, 12. Thereafter, the surgeon may remove the insertion tool 250thereby completing the implantation of the intervertebral stabilizer 100into the intervertebral space. Appropriate closure procedures may thenbe carried out.

With reference to FIGS. 38 and 39, the surgeon may extract and/orreposition the intervertebral stabilizer 100 after implantation into theintervertebral space. In this regard, an extractor 350 may be utilized.The extractor 350 preferably includes a handle 352 having proximal anddistal ends 354, 356, respectively. The extraction tool 350 preferablyfurther includes an engagement element 358 depending from the proximalend 356. The engagement element 358 is preferably operable toreleaseably engage the stabilizer 100 after it has been positionedwithin the intervertebral space. More particularly, the engagementelement includes a longitudinally extending member 360 and atransversely extending member 362. The longitudinally extending member360 is preferably sized such that is may pass through one or more of theapertures 150, 152 (or any of the other aperture embodiments herein).The transversely extending member 362 is preferably sized to passthrough the slit 108 as the longitudinally extending member 360 isinserted into the aperture, for example, aperture 150. Thelongitudinally extending member 360 is preferably of sufficient lengthto cause the transversely extending member 362 to enter the hollowportion 120 of the body 106. Thereafter, the surgeon preferably rotatesthe handle 352 of the extraction tool 350 such that the transverselyextending member 362 engages an interior surface of the hollow portion120 such that the stabilizer 100 may be pulled by the handle 352 of theextraction tool 350.

In an alternative embodiment, the engagement element 358 includes athreaded portion (not shown) that may be screwed into a threadedaperture in order to engage the stabilizer. For example, the aperture158 (FIG. 15) of the stabilizer element 100B may be threaded and theengagement element 358 of the extraction tool 350 may be threaded intothe aperture 158 to permit the surgeon to reposition and/or extract thestabilizer element 100B.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. A cervical intervertebral stabilizer for a cervical region of aspine, comprising: a first surface operable to engage an endplate of afirst vertebral bone of a spine; a second surface spaced apart from thefirst surface and operable to engage an endplate of an adjacent secondvertebral bone of the spine; and a spring element including asubstantially solid exterior wall forming a hollow passage between thefirst and second surfaces, the solid exterior wall including at leastone helical slit therethrough forming a plurality of annularcircumferential, overlapping helical coils, the spring element beingdisposed between the first and second surfaces and operable to providereactive force in response to compression loads from the first andsecond vertebral bones, wherein at least some diameters of respectiveturns of the helical coils differ such that those of the turns havinglarger diameters are disposed towards the first and second surfaces andthose of the turns having smaller diameters are centrally locatedbetween the turns having larger diameters, and diameters of the hollowpassage between the first and second surfaces vary such that largerdiameters are disposed towards the first and second surfaces and smallerdiameters are centrally located.
 2. The cervical intervertebralstabilizer of claim 1, wherein the spring element includes one of (i)about 3.0 grooves or 4.0 coils; and (ii) about 4.0 grooves or 5.0 coils.3. The cervical intervertebral stabilizer of claim 2, wherein a heightbetween the first and second surfaces is one of: (i) about 5.0 mm to 7.0mm when the spring element includes about 3.0 grooves or 4.0 coils; and(ii) about 7.0 mm or 9.0 mm when the spring element includes about 4.0grooves or 5.0 coils.
 4. The cervical intervertebral stabilizer of claim3, wherein it is sized and shaped for an intervertebral space in thecervical region of a spine.
 5. The cervical intervertebral stabilizer ofclaim 1, wherein a cross-sectional profile taken through the springelement is at least partially hourglass shaped.
 6. The cervicalintervertebral stabilizer of claim 5, wherein the cross-sectionalprofile taken through the spring element has a multiple hourglass shape.7. The cervical intervertebral stabilizer of claim 1, wherein at leastone of: the first surface includes a peripheral edge that overhangs atleast one coil of the spring element; and the second surface includes aperipheral edge that overhangs at least one coil of the spring element.8. The cervical intervertebral stabilizer of claim 7, wherein at leastone of: a first moment arm is defined by a lateral distance between anouter surface of the at least one coil of the spring element and theperipheral edge of the first surface; and a second moment arm is definedby a lateral distance between the outer surface of the at least one coilof the spring element and the peripheral edge of the second surface. 9.The cervical intervertebral stabilizer of claim 8, wherein at least oneof the moment arms defined by the hourglass shape operates such that: acompressive force acting on one of the peripheral edges and the other ofthe first and second surfaces tends to collapse the spring element andfull compression of the spring element in response to the compressiveforce results in adjacent coils engaging one another; and furthercompressive force acting on only a portion of the peripheral edge tendsto cause the adjacent coils to engage one another and to expand portionsof coils on an opposite side of the spring element from the engagedcoils.
 10. The cervical intervertebral stabilizer of claim 1, furthercomprising: at least a pair of apertures operable to receive aninsertion tool for implanting the stabilizer into a patient, wherein alongitudinal axis of the stabilizer is normal to the first and secondsurfaces and the apertures extend transverse to the longitudinal axis.11. The cervical intervertebral stabilizer of claim 10, wherein thefirst and second apertures extend only partially into the hollow bodysuch that slots are formed at the first and second surfaces.
 12. Thecervical intervertebral stabilizer of claim 11, wherein the at least onepair of apertures are longitudinally spaced apart such that the firstaperture of the pair is disposed at the first surface and the secondaperture of the pair is disposed at the second surface.
 13. The cervicalintervertebral stabilizer of claim 12, further comprising one or morespikes extending from at least one of the first and second surfaces andalong at least one of the slots, the spikes for promoting engagement ofthe stabilizer with the associated vertebral bones.
 14. The cervicalintervertebral stabilizer of claim 1, further comprising one or morebone adhesion facilitating elements operable to promote bone adhesion toat least one of the first and second surfaces, wherein the one or morebone adhesion facilitating elements includes at least one of: one ormore spikes extending from at least one of the first and second surfacesfor promoting engagement thereof with the associated vertebral bones;one or more keels extending from at least one of the first and secondsurfaces for promoting engagement thereof with the associated vertebralbones; and one or more roughening elements one at least one of the firstand second surfaces for promoting engagement thereof with the associatedvertebral bones.
 15. The cervical intervertebral stabilizer of claim 1,wherein: the first surface includes a peripheral edge that overhangs atleast one coil of the spring element; a moment arm is defined by alateral distance between an outer surface of the at least one coil ofthe spring element and the peripheral edge of the first surface; and thepassage is sized and shaped to maximize a length the moment arm.
 16. Thecervical intervertebral stabilizer of claim 15, further comprising amembrane disposed in the passage and substantially closing off thepassage to inhibit bone growth therethrough.
 17. The cervicalintervertebral stabilizer of claim 16, wherein the membrane is formed asan integral element of the hollow body.